Excitatory amino acid concentrations in the spinal dorsal horn of
cats during muscle contraction.
Hand, Gregory A., Gerald L. Kramer, Frederick Petty, George A. Ordway,
and L. Britt Wilson.
The Harry S. Moss Heart Center and Departments of Physiology and
Psychiatry, University of Texas Southwestern Medical Center, Dallas,
TX 75235-9040
APStracts 3:0113A, 1996.
In anesthetized cats, static hindlimb muscle contraction reflexly
increases mean arterial pressure (MAP) and heart rate (HR).
Pharmacological and immunohistochemical evidence suggests that
excitatory amino acids are involved in the spinal transmission of
this reflex. Using microdialysis and HPLC technology, we tested the
hypothesis that static contraction of the triceps surae muscle
increases the extracellular concentration of glutamate (GLU) and
aspartate (ASP) in the L7 level of the dorsal horn of the spinal
cord. With the exception of the L7 dorsal root, the L5-S2 dorsal and
ventral roots were cut ipsilateral to the contracting muscle. After
the insertion of microdialysis probes and a three-hour recovery
period, a two-minute static contraction was electrically evoked. MAP
and HR increased by 53+/-8 mmHg and 20+/-4 bpm. The concentration of
GLU increased from 324+/-59 to 857+/-80 nM, while ASP increased from
199+/-57 to 499+/-113 nM. These results were repeatable in that GLU
and ASP rose by similar amounts in 2 subsequent contractions. In both
of these latter contractions, MAP and HR were also significantly
increased. By contrast, in a subset of cats whose L7 dorsal roots
were cut after the first contraction, neither MAP, HR, GLU, nor ASP
were significantly increased over baseline levels. These data
demonstrate that static contraction of the hindlimb increases the
extracellular concentration of GLU and ASP in the dorsal horn. In
summary, the results from this study are in agreement with previous
findings suggesting that excitatory amino acids are involved in the
spinal transmission of sensory information from the hindlimb muscle.
Received 20 September 1995; accepted in final form 12 February
1996.
APS Manuscript Number A1019-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96